Addition reactions are a type of chemical reaction where two or more substances combine to form a single product. This process typically involves unsaturated compounds, such as alkenes and alkynes, which contain double or triple bonds. When these bonds break, new atoms or groups are added, resulting in a saturated compound. These reactions are important in organic chemistry and are commonly used in the synthesis of various compounds, including plastics, fuels, and pharmaceuticals. Addition reactions can be categorized into several types, such as hydrogenation, halogenation, and hydrohalogenation, each involving different reactants and conditions.